Revised SSE2 color conversion
Revised SSE2 color conversion

I discovered there's average and shuffle instructions which simplify the
calculations of UV components. Also the extract instruction was very useful.

In terms of the algorithm I rearranged the memory reads to be sequential.

Overall this gives about 10% improvement on 64-bits machine.

On 32-bits machine this gives 20% improvement. If compiled as 32-bits code this is
quite slow compared to 64-bits, about 2x slow down. So working on MMX code will
be a direction for improvement.

BUG=None
TEST=I tried it, it looks right.

Review URL: http://codereview.chromium.org/6488014

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@74827 0039d316-1c4b-4281-b951-d872f2087c98

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